Vestigial flies

We are undertaking a basic high school lab crossing homozygous wild with
homozygous vestigial. We expected a 3:1 ratio at the end of the second
generation but we ended up with a 5:1 ratio. We realize that this could
occur naturally but we were wondering if the development rate of the
vestigial flies might be slightly different from the wild flies and if
this is true why might it occur ? Also the female count was much larger
than the male count.